Emulsion Acid Diversion Agents for Oil Wells Containing Bottom Water with High Temperature and High Salinity

[Image: see text] Conventional acid diversion agents cannot tolerate the high temperature and salinity of acidizing water-producing oil wells that contain bottom water and heterogeneous layers. Therefore, a water/oil (w/o) emulsion was proposed as an acid diversion agent to promote acidification. The selected emulsifier, oleic acid imidazoline, is a switchable emulsifier. Because this emulsifier reacts with acids to transform amines into ammonium, the emulsion rapidly demulsifies, and the emulsion acid diversion agent can use the spent acid flowback to remove plugging. Evaluation of the emulsion properties indicated that a 10 wt % emulsifier generated a stable emulsion at oil/water ratios from 1:9 to 4:6 at 90 °C. Viscosity was higher at lower oil/water ratios, and the emulsion with an oil/water ratio of 4:6, which had a low viscosity, was injected into the formation. During injection, the emulsion continued to emulsify in high-permeability channels, which increased the viscosity until the water layer was blocked. During experiments, single-tube and dual-tube models were designed to evaluate the injectivity and plugging selectivity of this emulsion. The results showed that the resistance factors exceeded 14 in the high-permeability cores when the emulsion was injected. The higher permeability ratio in parallel cores allowed a larger emulsion volume to enter the high-permeability cores. In experiments using parallel cores, the block rate of the high-permeability cores exceeded 92%, and that of the low-permeability cores was less than 12%. Finally, this emulsion was injected into two groups of parallel carbonate cores for acidification diversion tests. The results indicated that the permeability of the acidified low-permeability core was basically the same as that of the high-permeability core plugged by the emulsion. The findings of this study improve the understanding of the feasibility and advantages of using emulsions as acid diversion agents for high-temperature and high-salinity oil wells containing bottom water.